Light controlled oscillator-automatic headlamp dimmer system



1958 G. w. ONKSEN LIGHT CQNTROLLED OSCILLATOR-AUTOMATIC HEADLAMP DIMMER SYSTEM Filed Jan. 1956 nited States LIGHT CONTROLLED OSCILLATOR-AUTOMATIC HEADLAMP DIMMER SYSTEM Application January 5, 1956, Serial No. 557,488

8 Claims. (Cl. 315-83) This invention relates to light sensitive switching means and more particularly to light sensitive switching means that is particularly adapted for use in automotive vehicles for changing from high to low beam energization. Automatic light sensitive control means for headlamp beam illumination actuated in response to approaching light intensity is currently available on the market. However, this equipment utilizes components that require relatively high voltage. This necessitates a separate power package which includes a current interrupter such as a vibrator and a step-up transformer in order to provide such voltage from a low voltage direct current source. This is an appreciable factor in the cost of the equipment.

It is an object in making this invention to provide light sensitive control means which is operable by voltages no higher than the voltage available from the vehicle power supply. such for example as the storage battery.

It is a further object in making this invention to provide a low voltage automatic headlamp dimming system that does not require a power pack for transforming the available voltage.

It is a still further object in making this invention to provide means for stabilizing the sensitivity of a low voltage light sensitive switching control means for changing the beam illumination in automotive headlamps.

With these and other objects in view which will become apparent as the specification proceeds, my invention will be best understood by reference to the following specification and claims and the illustrations in the accompanying drawings, in which the figure is a circuit diagram of a light sensitive control system embodying my invention.

Automotive vehicles are conventionally provided with dual filament headlamps which contain a long range or upper beam filament and a shorter range or lower beam filament. It is desired to utilize upper beam illumination as long as no cars are approaching from the opposite direction which would be bothered by high intensity light. Systems are available for vehicles which will maintain the headlamps on upper beam illumination, but when approached by light from the opposite direction will automatically switch to lower beam illumination, retaining that energization until the approaching light intensity has fallen below a certain level. In the present instance the cable 2 is shown which extends from the headlamps and contains three lines. Line 4 is connected to the storage battery of the vehicle, line 6 to the upper beam filaments, and line 8 to the lower beam filaments. A power actuated relay 10 is provided to switch from upper to lower beam illumination. This relay includes an operating coil 12 and a movable armature 14 which oscillates between two spaced stationary contacts 16 and 18. Contact 16 is electrically connected to line 6, and contact 18 to line 8. Power line 4 is connected to one end of the operating relay coil 12 and also to the relay armature 14. The latter is spring biased downwardly by biasing spring 20 connected between the armature 14 and some part of the framework. From this circuit it atent O p Zilfifildl Patented Dec. 23, 1.235.?

Will be obvious that when the relay coil 12 is energized, the armature 14 will be in its uppermost position, completing a supply circuit to the upper beam filaments, and when the armature 14 is in its lower position, it will likewise be supplying power to the lower beam filaments.

The energization of the power relay actuating coil 12 is controlled by the grounding circuit therefor which extends through a conventional foot dimmer switch 22 and a sensitive relay switch 24. This circuit is defined from the lower terminal of the relay coil 12 which is connected through line 26 to the movable arm 28 of the foot dimmer switch 22. This arm 28 may contact fixed contact 30 of said switch in one position. Contact 30 is connected through line 32 to stationary contact 34 of the sensitive relay 24. Movable armature 36 of the sensitive relay 24 is grounded and when it engages contact 34 it completes the grounding circuit. Thus when sensitive relay 24 is energized and when the standard foot dimmer switch 22 is in its left-hand position, power relay coil 12 will be energized.

The sensitive relay 24 includes an actuating coil 38 which attracts its armature into engagement with contact 34 when energized. When deenergized, the armature 36 is spring biased upwardly into engagement with spaced stationary contact 40 whose purpose is to change the bias on the system or the sensitivity thereof. One terminal of the coil 38 is connected through line 42 with the source of power such as the vehicle battery. The other terminal of the coil 38 is connected through line 44 with the plate 46 of an electron tube 48, the cathode 50 of which is grounded. Thus the energizing circuit for the relay coil 38 is through the electron tube and when that is so biased as to pass a sufficient amount of current, the coil will be energized. The unregulated power line 42 is connected through a variable resistor 52 to a regulated power line 54. A biasing resistor 56 is connected between line 54 and ground. A parallel biasing circuit including resistance 58 and a variable resistance 60 is provided in order to adjust the voltage on line 54.

A tie line 62 extends from the unregulated power supply line 42 to a voltage divider consisting of two resistances 64 and 66, the opposite terminal of which is connected to the lower potential regulated power line 54. The center tap between the two resistors 64 and 66 is connected to a further resistance 68 and thence through a condenser 70 to ground. A variable resistance 72 is connected to the intermediate point between resistance 68 and condenser 70 and the stationary contact 40 of the sensitive relay through line 74. The variable resistance 72 is provided in order to adjust that point in light intensity at which the system will switch back to high beam. Resistance 76 is connected between power line 42 and line 32. The screen grid 78 of the tube 48 is connected directly to line 54. It has been previously stated that the energization of the sensitive relay coil 38 is dependent upon the current flow through the tube 48. Therefore when that tube conducts and the sensitive relay coil 38 is energized to attract its armature 36, the power relay coil 12 will be energized and the lights on high beam.

The control system for determining the conductivity of the tube 48 consists of a photoelectric cell 80 which controls a pre-amplifier including tube 82. The output of the pre-amplifier is amplified through a stage including tube 84 and then applied to a free-running multivibrator including double triode tube 86. When no light falls on the phototube, the tube 82 will be nonconductive and the voltage on the plate will be relatively high to provide a high positive bias on tube 84 and that tube will be conducting. The plate voltage of tube 84 will thus be low, impressing a low voltage on the first control grid of the tube 86, and the multivibrator will be non-oscila latory. At this point the tube 48 is so biased as to conduct a suflicient amount of current to energize the relay coil 38, causing it to attract its armature 38 and maintaining the lights on high beam.

The details of this system disclose that the plate 88 of the preamplifier tube 82 is connected through a variable resistance 90 to a point intermediate the resistor 68 and condenser 70. The adjustment of this resistance 90 will vary the plate voltage and determine the point at' which the system switches from high beam to low beam. The cathode 92 of the photocell 86 is connected to the control electrode 94 of the pre-amplifier tube 82. The anode 96 of the photocell is connected directly to the cathode 98 and to ground. The plate 88 is connected directly to the control grid 100 of the second amplifier stage 84 by line 102.

Supply line 54 is connected to a further reduced voltage supply line 104 by dropping resistor 106. A filter condenser 108 is connected between line 104 and ground. The plate 110 of the tube 84 is connected through limiting resistor 112 to supply line 104 for its plate voltage. A voltage divider consisting of two resistances 114 and 116 in series is connected between line 104 and ground. Screen grid 118 of tube 84 is connected directly to line 104. An adjustable tap 120, movable over resistance 116, is connected to the cathode 122 of tube 84 and provides a means for adjusting the cathode bias voltage of this tube. Two resistances 124 and 126 are connected in series between plate 110 and ground and the center point between these two resistances'is directly connected to control grid 128 of the first section of the duo-triode tube 86.

Plates 130 and 132 or the tube 86 are connected through limiting resistances 134 and 136 respectively to supply line 104 to provide plate voltage. Plate 132 is coupled back to control grid 128 of the first section by condenser 138. In like manner plate 130 of the first section is coupled to control grid 140 of the second section by coupling condenser 142. Cathode 144 of the second section is directly connected to ground. The cathode of the first section is, however, maintained at a predetermined bias. A voltage divider consisting of resistors 146 and 148 in series is connected between supply line 104 and ground. Cathode 158 of the first secfion of tube 86 is connected to a point intermediate the two resistances 146 and 148 and assumes the voltage of that point. A radio frequency bypass is provided by condenser 152 which is connected between the cathode and ground. The control grid 14-0 is also connected to line 104 through a limiting resistor 154-.

The output of the oscillator is capacity coupled through condenser 156 to control. grid 158 of the power amplifier tube 48. In order to insure more positive operation of the power amplifier stage in changing conductance, a rectifying diode 1.60 is provided connected as shown. The plate 162 of the diode 16th is connected through a resistance 164- to the control grid 158 of the tube. The plate is also connected through resistance 166 to ground. A bypass condenser 168 is connected in parallel with the resistance 166 between the plate 162 and ground. Cathode 17d of the tube is connected through biasing resistor 172 to ground and also through a coupling condenser 174 to the plate 46 of the power amplifier tube 48. As the conductance of tube 48 is reduced, a pulse is applied to the rectifier 160 which conveys a further negative pulse to grid 158 to assist in cutofi.

In order to maintain the sensitivity of the system substantially constant, it is necessary to maintain the screen voltage of the pro-amplifier tube 82 within limits, both maximum and minimum. The improvement in the present system, therefore, lies in the application of the double diode tube 176 and the potentiometer supplying power thereto for regulating the voltage on the screen grid 178 of the pre-amplifier tube 82. A potential divider comprising three resistances 186, 182 and 184 is connected in series between line 104 and ground. An adjustable tap 186 movable over resistance is connected to the cathode 188 of the second diode section of the tube 176. An adjustable tap 190, movable over resistance 182, is connected directly to plate 192 of the first diode section of the tube. The cathode 194 of the first diode section and the plate 196 of the second diode section are connected together and to the screen grid 178 of the tube 82.

In the operation of this system, when the lighting switch is turned on energizing the 12-volt lines, and after the tubes have had a chance to warm up, with no light falling on the photocell 80 the system is so biased that the power amplifier tube 48 conducts a sufficient amount of current to energize relay coil 38 and attract its armature 36 to hold it in contact with the stationary contact 34. Assuming that the manually operated switch 22 is placed in the position shown in the figure, an energizing circuit is thus completed for the power relay as follows: from the 12-volt line 4, relay coil 12, line 26, switch arm 28, contact 30, line 32, contact 34, armature 36 to ground. With coil 12 energized it attracts its armature 14 to engage stationary' contact 16, completing an obvious circuit to the upper beam filaments through line 6. As long as the incident light upon the photocell 80 does not exceed a predetermined value, the system remains in this condition with the upper beams energized. Of course, at this time operation of the manual switch 22 to open the contacts 28-30 will interrupt the energizing circuit for relay coil 12 and cause it to drop its armature, switching to low beam. A return of the manual switch 22 to the position shown will again energize the high beam filamerits.

If the amount of incident light falling on the photocell 80 exceeds a predetermined value, then the bias on grid 94 will vary to increase the conductance through tube 82 and thus lower the plate voltage on plate 88. This in turn lowers the voltage on control grid 100 of the amplifier 84, causing this tube to decrease in conductivity and therefore increasing the plate voltage of plate 110. This voltage affects the voltage on control grid 128 of the first half of the multivibrator, increasing that voltage, allowing the first section to conduct, and setting the oscillator into operation in conventional free-running multivibrator operation. As long as the incident light on the photocell 80 exceeds a predetermined value, the oscillator will continue to run. The output of said oscillator is connected through coupling condenser 156 and is applied in a series of pulses to control grid 158 of the power amplifier tube 48. Due to the rectifying action of the gridcathode section of this tube, these pulses build up a negative biasing voltage on said grid, causing the conductivity of tube 48 to decrease to a point Where it causes the relay coil 38 to drop its armature, breaking the grounding circuit for power relay 12, previously traced, and causing armature 14 to be pulled downwardly by spring 20 to engage contact 18, thus switching automatically to low beam energization. The rectifier tube 160 receives a pulse from the plate 46 when the tube 48 cuts off, which pulse is rectified and applied back to the control grid 156 to give it a more positive cutoff action.

When the light on the photocell decreases below a second predetermined light intensity level, the grid 94 of the pre-amplifier returns to a negative bias, cutting off conduction through tube 82, which in turn raises the plate voltage thereof and also the voltage of control grid 100 of tube 84. This increases the flow through tube 84 to in turn decrease the plate voltage of plate 100 and thus cut off the multivibrator oscillator. When this ceases to oscillate, control grid 158 of power tube 48 rises to permit conduction through that tube and a reenergization of relay coil 38 to attract its armature 36, which again completes the energizing circuit for relay coil 12 and the lights switch back to high beam.

When the amount of light falling on the photocell in an ordinary car installation is sufiicient to cause a switching from high to low beam, it is customary for the approaching car from which said light originates to in turn dim its headlights. This causes a considerable reduction in the amount of incident light only slightly after the automatic system has switched due to a given light level. Unless some means are provided, the system would return to high beam illumination to cause an alternate flashing and unsatisfactory operation. The present system utilizes a change in sensitivity of the amplifier in order to overcome this difficulty. The system is many times as sensitive after it has switched to low beam position than it is before switching. This change in sensitivity is obtained by switching in and out a resistance 72 in the plate supply circuit for preamplifier tube 82. Resistance 72, which is adjustable, is connected to back contact 40 of the sensitive relay 24. Also in this same plate supply circuit there is provided an adjustable resistance 90. The adjustment of resistance 90 is set to determine the point at which the system switches from high to low beam or what may be referred to as the dimming sensitivity. Adjustment of the resistance 72 on the other hand determines the point at which the system will switch back from low to upper beam and is referred to as the hold sensitivity. Thus, when the sensitive relay is deenergized to cause switching to lower beam, at the same time resistance 72 is inserted into the plate supply circuit and increases the sensitivity of the amplifier many times.

Since the system is operative on low voltage, any fluctuations applied particularly to the pre-amplifying tube 82 will cause a variation in operation which is undesirable. Fluctuations in the voltage on screen grid 78 are in this category, and it is desired to hold the screen grid voltage at least between certain limits of fluctuation. The screen grid voltage will vary somewhat upon changes in conductance through the tube due to current flow through resistance 198 which is connected between the screen grid and the supply line 104. These variations are dampened by condenser 200 which is connected between the screen grid'178 and ground. However, in order to keep the fluctuations of the screen grid 178 within limits, I have utilized the double diode tube 176. One diode section is connected to determine the upper limit of voltage which can be applied to the grid without the diode conducting and diverting current to limit such variation and the other diode section is adjusted to determine the lower limit and will conduct to divert current if the voltage tends to go below a predetermined amount.

These adjustments are obtained by moving the adjustable taps 186 and 190 over resistances 180 and 182 respectively. Thus if the voltage on the screen grid tends to exceed a given voltage, the diode 188196 will conduct at that voltage, thus diverting current from the screen grid and preventing the voltage thereon from exceeding a given value. The second diode 192-194 operates in the same manner upon a reduction in voltage below a certain point. Thus the double diode provides limits for the voltage on the screen grid. This provides a stabilizing action on the operation of the set.

If at any time when the automatic light sensitive system is controlling, the beam illumination and the amount of incident light defines low beam energization, and the operator desires high beam illumination, overriding means is provided. This is through a limiting resistor 202, one terminal of which is connected to line 44, and the opposite terminal to line 204 which extends to a grounding switch. Closure of that switch (not shown) completes an obvious circuit through the sensitive relay coil 38 to ground, exclusive of any conduction through the power amplifier tube 48.

I claim:

1. In a light sensitive control system, photoelectric means, amplifying means connected to the photoelectric means, said amplifying means having a control electrode to adjust the conductivity thereof, a low voltage source of electrical power connected to said electrode and voltage regulating means independently connected between the source of power and said electrode to prevent the voltage thereon from exceeding either upper or lower limits.

2. In a light sensitive control system, photoelectric means, amplifying means connected to said photoelectric means to amplify the output thereof, a control electrode in said amplifying means to adjust the conductivity thereof, a source of electrical power and means connected to the source of power and the electrode for providing a plurality of separate paths including some having rectifying means therein for maintaining the voltage applied to the control electrode between predetermined limits.

3. In a light sensitive control system, photoelectric means, an amplifying tube having a plate, cathode and plurality of grids, said photoelectric means being connected between one of the grids and the cathode, a source of electrical power connected to another grid, and voltage regulating means connected between said source of power and said other grid including a plurality of rectifiers connected in inverse relation to maintain the voltage applied thereto between predetermined limits.

4. In a light sensitive control system, photoelectric means, an amplifying tube having a plate, cathode and purality of grids, said photoelectric means being connected between one of the grids and the cathode, a source of electrical power connected to another grid including a plurality of rectifiers connected in inverse relation, voltage regulating means connected between said source of power and said other grid to maintain the voltage applied thereto between predetermined limits, and a condenser connected between the other grid and ground.

5. In a light sensitive control system, photoelectric means, an amplifying tube having a plate, cathode and plurality of grids, said photoelectric means being connected between one of the grids and the cathode, a source of electrical power connected to another grid, a potentiometer connected to the source of power and a plurality of rectifier means connected in inverse relation and to different positions on said potentiometer and to the other grid to limit the voltage applied thereto.

6. In a light sensitive control system, photoelectric means, an amplifying tube having a plate, cathode and plurality of grids, said photoelectric means being connected between one of the grids and the cathode, a source of electrical power connected to another grid, a potentiometer connected to the source of power having a plurality of variable taps thereon, and a plurality of rectifiers connected in opposite relationship between the variable taps and the other grid.

7. In a light sensitive control system, a low voltage supply of electrical power, an electron amplifier means having a plurality of control electrodes and an output circuit, one side of which is grounded, a photosensitive element connected between one control electrode and ground, a voltage divider having a plurality of adjustable taps and a plurality of rectifiers connected in opposite phase to the taps and to another control electrode of the electron amplifier means to maintain the voltage on the other control electrode between defined limits regardless of the variation in the supply voltage.

8. In a light sensitive control system, a low voltage source of electrical power, electron amplifier means having a plurality of control electrodes, an output and an input circuit, said input circuit being connected to one of said electrodes, a light sensitive unit connected to said input circuit and varying the conductance through the electron amplifier means depending upon the amount of light falling on said unit, resistance means connected between the low voltage power source and ground, adjustable taps on said resistance, and a plurality of rectifier means connected independently between said taps and another control electrode of the electron amplifier means in opposite relation to control the voltage on said other controi electrode between defined limits regardless of the variation of the low voltage source.

References Cited in the file of this patent UNITED STATES PATENTS Edwards et a1. July 11, 1933 Shepard Nov. 30, 1937 Atkins June 29, .1954 

